Apparatus for well stimulation



May 24, 1966 J. C. SOLAR] ETAL APPARATUS FOR WELL STIMULATION Original Filed June 29. 1961 4 Sheets-Sheet 1 PRESSURE PRESSURE -D:$TANE FROM WELL soRE FIG. 2

PRESSURE -z "DISTANCE FROM WELL BORE- FIG.3 INVENTORS DARRELL C. GALLEAR JOSEP C. SOLAR! ATTORNEYS May 24, 1966 J. c. SOLAR! ETAL APPARATUS FOR WELL STIMUDATION 4 Sheets-Sheet 2 Original Filed June 29. 1961 PRESSURE 30/ }1 DISTANCE FROM WELL BORE FIG.4

PRESSURE PRESSURE iDlSTANCE FROM WELL BORE FIG.5

IDISTANCE FROM WELL BORE-D INVENTORS DARRELL C. GALLEAR JOSEPH C SOLAR/ BY .fsaokwswm ATTORNEYS FIG.6

y 1966 J. c. SOLARI ETAL 3,252,519

APPARATUS FOR WELL STIMULATION INVENTORS DARRELL C. GALLEAR JOSEPH C. SOLAR! ATTO May 24, 1966 J. c. SOLAR] ETAL APPARATUS FOR WELL STIMULATION 4 Sheets-Sheet 4 Original Filed June 29, 1961 FIG.|O

F'IGJI FIG. l3

FIGJS INVENTORS DARRELL C. GALLEAR JOSEPH C. STZLARI FIG.I2

ATTORN EYS United States Patent 3,252,519 APPARATUS FOR WELL STlMULATlON Joseph C. Solari and Darrell C. Gallear, Taft, Calif., as-

signors to Chevron Research Company,a corporation of Delaware Original application June 29, 1961, Ser. No. 120,603. Divided and this application Apr. 13,1965, Ser. No.

2 Claims. c1: 166-226) cause of poor fluid flow from the producing formation into the production well. A prime cause of this sluggish fluid flow is plugging of the producing formation or of the production liner in the well adjacent the producing formation by unconsolidated or semiconsolidated foreign matter. For example, unconsolidated fine formation rock material deposited near the producing well may subsequently retard fluid flow by bridging. Deposition of asphalt or asphalt products in the formation surrounding the producing well is also a commonly encountered problem. These problems are particularly troublesome in wells located in low pressure formations or in wells located in higher pressure formations where the available drawdown differential between the formation and the producing well is incapable of removing fluid flow restrictions from the perforations of a well liner or from the formation.

One method heretofore known in the art and directed at improving fluid flow into a producing well from a formation is taught in US. Patent No. 2,361,558. As there disclosed, a sharp liquid surge is provided in a well by means of positioning a pressure-resistant frangible fluid filled container at a desired elevation in a well and fracturing the container to create a low pressure area in the liquid in the well to effect a surge of liquid from all directions by the compression of the gaseous fluid by the liquid column in the well. The method as taught therein depends on the height of the liquid column in the well to provide the hydraulic surge. As the frangible container is fractured, the liquid column in the well is left unsupported and it falls into the low pressure void thereby created. When the liquid column strikes the bottom of the space occupied by the low pressure fluid, a tremendous force is suddenly exerted on the well which absorbs the kinetic energy of the falling liquid column. The theory is that the fluid production from the well will be improved by means of the hydraulic surge therein created. Frequently, however, the sudden force exerted on the well, as described above, causes damage to the formation walls and doe little to improve fluid flow therefrom.

Another method practiced in the prior art to improve oil recovery from a producing formation has been the use of pressure bailers. The pressure bailer, as known in the art, utilizes the pressure differential between the well bottom and the interior of the bailer to cause a vacuumcleaner-like action on the debris located at the bottom of the well. This is accomplished by lowering the pressure bailer, the interior of which is usually at atmospheric pressure, to the bottom of a liquid filled Well. The pressure bailer is then opened to the bottom hole pressure so that liquid at the bottom of the well will enter and the resulting inrush of liquid carries with it debris accumu- 3,252,519 Patented May 24, 1966 lated on the bottom of the Well. The bailers are generally used to remove debris which has fallen into the well from unconsolidated formations penetrated by the well. The pressure bailers are not primarily a stimulation tool; however, if one were to be used as a stimulation tool, the falling fluid column would again create a sudden force on the well. If a bailer is allowed to gradually take in liquid to prevent the sudden force on the well caused by the falling fluid column, the hydraulic surge effect is not great enough to promote fluid flow from the formation.

It is an object of the present invention to provide apparatus to create a relatively low pressure zone in a Well selectively communicable with a preselected higher pressured producing formation, opening the relatively low pressure zone to communicate with the higher pressured formation while simultaneously isolating the fluid column in the well above the relatively constant low pressure zone, thereby causing a hydraulic surge in the well, the principal portion of said surge coming from the producing formation.

It is a further object of the present invention to provide apparatus for promoting fluid flow from a producing formation by means of a hydraulic surge from said formation wherein the hydraulic surge may be repeated at plurality of times without removing the apparatus from the well.

Briefly, the present invention provides for improving fluid flow from a producing formation by causing a hydraulic surge from the formationby first establishing a zone of relatively constant pressure in a liquid column in a well selectively communicable with said formation,

increasing the pressure on said formation, suddenly caus-.

ing communication between said formation and said zone of relatively constant pressure and simultaneously isolating said zone of relatively constant pressure from the liquid column in the well to create a hydraulic surge, the principal portion of which comes from the producing formation.

Additional advantages and objects of the present invention will become apparent from the following detailed description and the accompanying drawings which are made a part of the present specification.

FIGS. 1 through 6 diagrammatically illustrate one form of apparatus during the successive steps of the invention with graphic indications of the pressure differentials between the formation and the well.

FIG. 7 is a vertical View partially in section of an embodiment of apparatus useful in practicing the method of the present invention, said apparatus positioned to remove fluids from the annulus between the well casing and the well tubing.

FIG. 8 is a vertical view partially in section of the same embodiment of apparatus, said apparatus positioned to permit fluid flow through well tubing into a selected formation.

FIG. 9 is a vertical view partially in section of the same embodiment of apparatus, said apparatus positioned to cause a fluid surge in the selected formation by permitting fluid flow from said selected formation into the annulus between the well casing and well tubing.

FIG. 10 is a sectional view at 1010 of FIG. 7.

FIG. 11 is a sectional View at 1 111 of FIG. 7.

FIG. 12 is a vertical view partially in section of a packer suitable for use with the embodiment of apparatus.

FIGS. 13, 14, and 15 are unrolled views of an improved locking cage in the packer illustrated in FIG. 12.

Referring specifically to FIG. 1, a well 10 is shown penetrating producing formation 12. The formation pressure near well 10 is represented by curve 16. The pressure scale for curve 16 is representative only and is not intended to indicate any particular formation pressures for which the method of the invention is useful.

3 FIG. 1 illustrates the production well 10 and the producing formation in a static condition prior to practicing the method of the invention, as if the well were shut in so that there is no pressure differential across the wall of the well.

FIG. 2 diagrammatically illustrates one embodiment of apparatus, useful in practicing the method of the present invention, positioned in well 10. The apparatus as shown comprises a pack-off means 20, a means for creating a relatively constant pressure zone as, for example, frangible pressure-resistant container 18, a tubing string 14 communicating with the surface, a valve seat means 22 and a valve means 24 arranged to allow for interruptible communication through tubing string 14 between the producing formation 12 and the surface and adapted to break frangible container. 18 when the valve means 24 seats.

As indicated by curve 16a the pressure on formation 12 is increased. This maybe accomplished in any suitable manner, for example, a liquid column may be established in tubing string 14. The liquid extends up tubing string 14 a predetermined distance to give a desired pressure increase on formation 12. "In many cases it is desirable not only to fill tubing 14 with liquid but also to pump liquid into formation 12 by means of pumps conmeeting to tubing string 14 at the surface. In this manner any reasonable pressure may be placed on the formation12.

In FIG. 3 curve 16b illustrates the pressure drop in formation 12 resulting from suddenly opening communication between the zone of constant pressure established by pressure-resistant frangible container 18 and the higher pressured producing formation 12. The frangible container '18 is shattered by the valve means 24 as it seats on valve seat 2 2. The valve means 24 may be actuated by any suitable means, for example, rod 28 dropped from the surface through tubing 14. Valve means 24 seats on valve seat 22 as it shatters frangible container 18. Therefore, the hydrostatic head of the liquid column in tubing string 14 above valve seat 22 is prevented-from damaging the formation or lessening the effect of the liquid surge from the formation by the liquid column falling into the void created by the shattered low pressure frangible container 18.

Pressure curves 16c, 16d, 162, and 16] in FIG. 4 illustrate the effect of isolating the newly created relatively constant pressure zone from the fluid column above valve seat 22. The resultingsurge of high pressure liquid into the lower pressured zone is primarily from producing formation 12. As indicated by curves 16c, 16d, 16e, and 16 there is no great force exerted on formation 12 caused by a falling fluid column.

FIGS; 5 and 6 illustrate the formation after completion of the hydraulic surge. In FIG. 5., debris 30 which has been removed from formation 12 is shown collecting on the bottom of well 10. Thetubing string 14 is pulled from well in a conventional manner. A conventional pressure bailer as described above may be run to clean the accumulated debris 30 from the bottom of well 10. In FIG. 6, well 10 and producing formation 12 are shown at the completion of the process. The producing well 10 is now ready for return to production.

Referring now to FIGS. 7, 8, and 9, an embodiment of apparatus is shown in the three positions required to perform the invention. As herein illustrated, SG-represents a well casing. The invention may be practiced in an uncased well, however, it is usually preferred in the art to case producing wells. The interior of casing 50 is packed off above a producing formation (not shown) by means of a packer 52. The pack-off is accomplished by means of packer element 53. The only communication therefore, between the producing formation and the surface of the earth is through tubing string 73, the surge stimulator assembly indicated as 60 and the interior of packer 52.

Lower lbody member 54 of the surge stimulator assembly 69 is secured to packer 52 by a suitable means such as the threaded joint at 55. Body member 54 is provided with a valve seating 57. Port means 58 are above valve seating means 57 and port means 58 are below valve Seating 57. Valve 61 is mounted-in the valve seat 57 and is spring loaded by spring 62 so as to be normally in a closed position, resistant to fluid flow from below.

Upper body member 63 is slidably mounted over lower body member 54. The body members 63 and 54 are desirably constructed to have tolerance .close enough to prevent the pasasge of high pressure fluid therebetween. The upper body member is provided with ports 65 and ports 66. By selectively positioning the upper body member 63 with respect to the fixed lower body member 54, ports 65 in upper body member 63 may. be selectively communicable with ports 58 in lower body member 54 and ports 66 in upper body member 63 may be selectively communicable with ports 59 in lower body member 54. Upper body member 63 is provided with valve seating 67 and valve means 68. The valve 68 is spring mounted by spring 69 in a normally open to flow position. The valve 68 in upper body member 63 is connected to valve 61 in lower body member 54 by means of wire line 70 and spring 71. Upper body member 63 is connected to a string of tubing 73 extending from the surface by means of a suitable connection such as threaded joint 74.

-The surge stimulator assembly 60 and packer 52 are preferably connected at the surface and are lowered into the borehole by means of tubing string 73. Packer 52 is positioned above the formation to :be stimulated and pack-01f element 53 is set to pack off the annulus between stimulator assembly 60 and. casing. from the formation.

Referring now specifically to FIG. '7, the surge stirnn. lator assembly is positioned as there shown by a downward force exerted on tubing 73 from the surface. after packer 52 has been set. By this adjustment lower body member 54 and upper body member 63 are positioned to allow communication between the interior of tubing string 73 and the annulus above packer elements 53, through ports and ports 58 and valve seat 67. Valve 61 in lower body member 54 is in its normally closed position and valve 68 in upper body member 63 is opened to fluid flow. In this position, liquid in the. annulus will flow to the interior of surge stimulator assembly 60 through the communication provided by ports 58 and 65. From there the liquid may be pumped to the surface by means of a suitable pump inserted in the interior of tubing 73. The fluid in the annulus is removed in this manner to provide a zone of relatively low pressure selectively communicable with the producing formation below packer elements 53. I

In FIG. 8 the stimulator assembly 60 has been moved to its second position. This adjustment is accomplished by raising the tubing string 73 a predetermined distance at the surface. In this position there are no ports in line to open communication between the interior of the stimulator assembly 60 and the annulus. upper body member 63 is in its normal position which allows fluid flow through the valve. Spring loaded valve 6,1 in lower body member 54 is shown in the opened position. When the tool is in the position as shown in FIG. 8, the formationis pressurized by means of a liquid column which is established in tubing 73 and pressure applied thereon. The pressure applied to the liquid opens spring loadedvalve 61 to liquid flow into the formation to be stimulated. The formation is pressurized to a predetermined pressure. This pressure should be in excess of the static formation pressure and preferably should be in the'order of at least 200 psi. above the static formation pressure. I I

Referring now to FIG. 9, the surge stimulator assembly- Valve 68 in been expanded to their expandable limit by raising the tubing string 73 a predetermined amount to its highest position. Valve means 61 is closed to fluid flow up the interior of surge stimulator assembly 60 and the liquid column remaining in tubing string 73 is isolated from the constant pressure zone in the annulus by the surge stimulator assembly 60. Ports 59 in lower body member 54 and ports 66 in upper body member 63 are now open thereby allowing communication between the annulus and the producing formation. Since the annulus is at a low relatively constant pressure which is substantially atmospheric pressure and the formation is under an elevated pressure as heretofore described, a fluid surge is created from the formation. When pressurized fluid in the formation is suddenly relieved to the lower pressure annulus as shown in FIG. 9, the highly pressurized fluid in and about the formation suddenly surges through the stimulator tool into the annulus. This surge of fluid brings about the well stimulation as provided by the method of the invention. Since valve 68 is closed by cable 70 when the surge stimulator assembly 60 is expanded to maximum position, no damaging force is exerted on the formation by the hydrostatic head created by the fluid column in tubing 73 above the stimulator assembly 69.

FIG. is a section taken at 10-10 of FIG. 7 showing the casing 50, the upper body member 63, the lower body member 54, valve seat 57, valve means 61, and spring 62. As there shown, the path for fluid flow through valve seat 57 is illustrated.

FIG. 11 is a section 1111 of FIG. 7 showing casing 50, upper body member 63, valve seating 67, spring 69 and valve 68. through valve seat 67 is illustrated.

FIG. 12 is a vertical view partially in section illustrating an improved packer useful in the present invention. The improved packer is particularly useful when it is desired to stimulate at different producing horizons in a well without having to pull the tubing string out of the well after each stimulation. The packer as here shown may be run in on the tubing string with the stimulator tool, and the packer set, stimulation accomplished, the packer freed, the tool moved to a new location in the well and the cycle repeated.

The packer illustrated in FIG. 12 is similar to a CO Packer of the valveless, hook-wall type manufactured by Lane-Wells, Incorporated and shown on page 2916 of the Composite Catalog of Oil Field Equipment and Services, l95859, published by World Oil. Two important improvements, however, have been incorporated into that design to prepare the packer for use with the stimulator assembly.

In order that the packer may be set and then released it is necessary that the packer mandrel 83 is free to turn when the rubber packing rings 53 are expanded against the well wall or the casing. To allow the packer to rotate when the packing rings are expanded, bushings 81 are inserted between the mandrel 83 and the packing rings 53. The bushings 81 are preferably sized so that when the packing rings are fully expanded the bushings 81 contact each other and thus substantially completely separate the packing rings 53 and the mandrel 83.

The second improvement in the packer in FIG. 12 comprises important modifications in the locking cage 88.

The locking cage 88 is a flat curved surface extending around mandrel 83. The improvement in the locking cage 88 and the manner of utilizing the improved packer in the invention can be better understood by reference to FIG. 13, FIG. 14 and FIG. 15 along with FIG. 12. FIG. 13, FIG. 14 and FIG. 15 are views of the locking cage 88 as it would look if it were cut at A-A on FIG. 12 and unrolled from its position around mandrel 83. The improvement in locking cage 88 comprise constructing the locking cage with a flat lower surface indicated at 90. A notch 92 is the only break in the flat lower sur- As there shown, the path for fluid flow 6. face 90 of locking cage 88. The notch 92 is provided with rounded corners to facilitate engaging and disengaging dowel pin 87 when mandrel 83 is rotated inside the locking cage 88.

In operation, the packer is connected to the stimulator tool 60 by collar 52 and positioned at a desired location in a well bore. The slips 82 are locked in a retracted position by dowel pin 87 held in the angular notch 92 as illustrated in FIG. 13. The slips 82 are unlocked from this retracted position by turning mandrel 83 about oneeighth turn counterclockwise. Friction spring 86 then forces slips 82 against the casing 50 as mandrel 83 is lowered. Continued lowering of mandrel 83 with resulting application of weight sets the slips 82 firmly against the casing 50 and expands the packing rings 53 to form the pack-01f. By rotating mandrel 83 counterclockwise about one-fourth turn, the locking cage 88 and dowel pin 87 are in the relative position illustrated by FIG. 14 and the slips 82 and the packing rings 53 are locked in expanded position.

After the completion of the well stimulation procedure the mandrel 83 is rotated clockwise until the slips 82 are unlocked by dowel pin 87 engaging the angular notch in locking cage 88 as illustrated in FIG. 15. The slips may be disengaged by an upward motion of the tubing string and then retracted by the spring collar to the original retracted position. The slips 82 and the packing .rings 53 are now again locked in a retracted position. The stimulator assembly is ready to be repositioned and the operation repeated.

As is evident from the specification, the invention provides a novel method and apparatus for well stimulation. The invention having been fully described and illustrated, we claim:

1. Apparatus for well'stimulation comprising a tubing string, an upper body member operably connected to said tubing string, first port means in said upper body member, second port means in said upper body member, upper body valve means, said valve means normally open to fluid flow, a lower body member in concentric slidable relationship with said upper body member, first port means in said lower body member adapted to be selectively aligned with said first port means in said upper body thereby providing a first fluid flow path from the interior of said body members to the exterior thereof, second port means in said lower body member adapted to be selectively aligned with said second port means in said upper body member thereby providing a second flow path from the interior of said body members to the exterior thereof, lower body valve means, said valve means normally closed to liquid flow but adapted to open upon the downward flow of liquid under pressure, means for alternately placing said first port means in said upper body member and said first port means in said lower body member in communicable relationship and said second port means in said upper body member and said second port means in said lower body member in communicable relationship, said upper and lower body valve means adapted to close simultaneously upon the placement of said second port means in said upper and lower body members in communicable relationship and packing means in operable relationship with said lower body member, said packing means adapted to pack off the annulus between the exterior of said tubing string and said well wall.

2. Apparatus for improving fluid flow from a well comprising an upper body member, upper body valve means, first port means in said upper body member, second port means in said upper body member, a lower body member in concentric slidable relationship with said upper body member, first port means in said lower body member selectively communicable with said first port means in said upper body member thereby providing a first fluid flow path from the interior of said body members to the exterior thereof, second port means in said lower body member selectively communicable with of said body members to the exterior thereof, lower body valve means and means for alternately placing said first port means in said upper body member and said first port means in said lower body member in communicable relationship and said second port means in said'upper body member and said second port means in said lower member in communicable relationship, said upper and lower body valve means adapted to close simultaneously upon the placement of said second port means in said upper and lower body members in communicable relationship.

1,625,140 4/1927 Nietzel l66-152 CHARLES E. OCONNELL, Primary Examiner. 

2. APPARATUS FOR IMPROVING FLUID FLOW FROM A WELL COMPRISING AN UPPER BODY MEMBER, UPPER BODY VALVE MEANS, FIRST PORT MEANS IN SAID UPPER BODY MEMBER, SECOND PORT MEANS IN SAID UPPER BODY MEMBER, A LOWER BODY MEMBER IN CONCENTRIC SLIDABLE RELATIONSHIP WITH SAID UPPER BODY MEMBER, FIRST PORT MEANS IN SAID LOWER BODY MEMBER SELECTIVELY COMMUNICABLE WITH SAID FIRST PORT MEANS IN SAID UPPER BODY MEMBER THEREBY PROVIDING A FIRST FLUID FLOW PATH FROM THE INTERIOR OF SAID BODY MEMBERS TO THE EXTERIOR THEREOF, SECOND PORT MEANS IN SAID LOWER BODY MEMBER SELECTIVELY COMMUNICABLE WITH SAID SECOND PORT MEANS IN SAID UPPER BODY MEMBER THEREBY PROVIDING A SECOND FLOW PATH FROM THE INTERIOR OF SAID BODY MEMBERS TO THE EXTERIOR THEREOF, LOWER BODY VALVE MEANS AND MEANS FOR ALTERNATELY PLACING SAID FIRST PORT MEANS IN SAID UPPER BODY MEMBER AND SAID FIRST PORT MEANS IN SAID LOWER BODY MEMBER IN COMMUNICABLE RELATIONSHIP AND SAID SECOND PORT MEANS IN SAID UPPER BODY MEMBER AND SAID SECOND PORT MEANS IN SAID LOWER MEMBER IN COMMUNICABLE RELATIONSHIP, SAID UPPER AND LOWER BODY VALVE MEANS ADAPTED TO CLOSE SIMULTANEOUSLY UPON THE PLACEMENT OF SAID SECOND PORT MEANS IN SAID UPPER AND LOWER BODY MEMBERS IN COMMUNICABLE RELATIONSHIP. 